Apparatus for sorting objects according to color



L. C. THAYER March 9, 1965 APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR 6 Sheets-Sheet 1 Filed July 1'7, 1961 E'Il3 1 EIHHHHHII Ill INVENTOR LOUIS G. THAYER BY vlww ATTORNEY March 3 F565 L. c. THAYER 3,173,017

APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR Filed July 17. 1961 6 Sheets-Sheet 2 I800- OSO INVENTOR LOUIS O.THAYER ATTORNEY March 9, 1965 1.. c. THAYER 3,173,017

APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR 6 Sheets-Sheet 31 Filed July 17. 1961 F'IE El I II?! 7 Ac COMPONENT or PULSES av AVERAGE DC COMPONENT OF PULSES 0V FIE: ll 2- BL 'QE A e L 8A0 e SUM OF POTENTIALS AT SLIDER OF POTENTIOME'TER SUM OF POTENTIALS ACROSS POTENTIOMETER F 15-12 F'IE l:EI

0c PULSES (AVERAGE) -2v 8 0v g i P -2v (A BEE '\I\1\/\+|20 KR /FOTENTIOMETER fl A0 AT mo RANGE KR2 KR2 INVENTOR LOUIS G.THAYER ATTORNEY ACTUAL CURVE L. C. THAYER March 9, 1965 APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR 6 SheetsSheet 4 Filed July 17. 1961 March 9, 1965 c. THAYER 3,173,017

APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR Filed July 17, 1961 6 Sheets-Sheet 5 w T'IE IEI INVENTOR LOUIS C. THAYER BY M444 ATTORNEY March 9, 1965 L. C. THAYER APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR Filed July 17, 1961 6 Sheets-Sheet 6 WITH SERIES FILTER IF K3 IS ZERO, Rl-RZ K2 RI+R2 TIE IIEI CRITICAL BIAS "7"\T";i 7 fi- 0c R2 R2 KR N T RI RI RI-R T h I i2 Fl-R2 I, I 2 1 I e i SOLVING FOR Kl V RI-R2 N0 SERIES FILTER 2 KRZ- Kl e PEAK TO PEAK=Rl-R2 IF KIIS ZERO.

RI R2 KRZ POS. HALF CYCLE a RI-RZ RI R2=2K 00 R2 INVENTOR LOUIS QTHAYER BY MM H M/ ATTORNEY United States Patent 3,173,017 APPARATUS FOR SORTING OBJECTS ACCORDING TO COLOR Louis C. Thayer, San Jose, Calitl, assignor to FMC Corporation, San Jose, Calif, a corporation of Delaware Filed July 17, 1961, Ser. No. 124,491 13 Claims. (Cl. 250-226) This invention relates to sorting objects in accordance with their color. Although the invention is particularly applicable to the sorting of citrus fruits such as lemons, oranges, grapefruit, or the like, so as to distinguish between fruit of various degrees of ripeness, in the broader aspects of the invention it is possible to apply its principles to other sorting operations, such as that of sorting tomatoes, apples, and other fruits and vegetables.

The invention will be described as it is applied to the sorting of lemons, although the invention is not limited to such an application. The lemon tree is an ever-bearing tree and usually has fruit in various degrees of ripeness or maturity growing thereon at the same time. It is not practical to harvest the fruit selectively, and consequently, fruit of various degrees of ripeness are harvested at the same time. Furthermore, even if it were desired to harvest the fruit selectively, the difficulty in distinguishing between the various degrees of maturity of the fruit increases as the fruit approaches maturity. In any event, a sorting operation is eventually required so that fruit of various grades can be stored together and the fruit of each grade brought to market at a period when that grade is ripe or mature.

The present invention sorts the fruit automatically into the various grades, and will not only sort fruit accurately when it is in its light or dark green state, but will distinguish between more mature fruit grades, the respective colors of which are less easily distinguishable.

The system employed in the present invention is that of sorting fruit by measurements made from light refiected by the fruit that is of two different wave lengths, namely, a wave length of light in the red portion of the spectrum and another in the infra-red. It has been found that where more than a few grades have been established, neither measurements based on a single wave length, nor those based on a difference in reflectances of two wave lengths, will provide dependable differentiation between all of the various grades for which classification is desired.

Where the sorting is based on a single reflectance, the signals are affected by the size of the object and so erratic results due to size variations are produced. Also, in the case of lemons the color criterion does not differ sufficiently between the more mature grades (silver and t yellow) to permit satisfactorily sorting with apparatus relying upon single reflectance.

Where the sorting is based on a comparison (difference) in the reflectances at two wave lengths, the percentage variations in signals from grade to grade have a total spread or a variation in magnitude such that when a number of grades are sorted, equipment having a very wide range is required. Furthermore, when the sorting is based on a comparison of reflectances at two wave lengths, the color criterion does not differ sufficiently between the light green and dark green grades to dependably attain commercial separation. It has been proposed in the patent to Powers, No. 2,933,713, April 19, 1960, to use a principle for sorting which not only reduces the effects of size of the object, voltage variations, and the like, but which renders relatively uniform the differences in the basis for classification that occur between the various successive grades. This improves the reliaice bility and accuracy of the sorting operation, and makes it possible to discriminate between all grades with commercial equipment. The index for sorting in such a system is a fraction, or ratio that will be termed the Index of Variation of Reflectance (IVR) ratio. The IVR ratio is a fraction, the numerator of which is the difference between the reflectances at two assigned wave lengths, and the denominator of which includes at least one of the individual reflectances. A system that sorts according to this fraction, or IVR ratio, has been found to provide color criteria between all grades of lemons, for example, that are sufficiently uniform in order or magnitude to permit commercial implementation. Also, since the index for sorting is a ratio, the IVR ratio system of color sorting renders the apparatus independent of such variables as changes in light intensity, changes in the characteristics of the photoelectric tube from time to time, and power supply fluctuations. Additionally, the IVR ratio system reduces the effects of differences in fruit size and of variations or blemishes in fruit color.

One of the objects of the present invention is to provide automatic color sorting, using the IVR ratio as a basis for the sorting wherein the division operation inherent in the ratio is performed directly by simple electrical means.

In the aforesaid Powers patent, a denominator adjustment, or electrical division, is performed by an automatic gain control system. If such systems are made sensitive enough to provide a small A.G.C. time delay, they border on oscillation, and oscillation is apt to occur if the time delay required by such systems is short enough to permit high speed operation. On the other hand, if the time delay required in automatic gain control circuits is made long enough to render the circuit stable, the sorting rate is correspondingly limited.

Another object of this invention is to provide a system wherein the articles are color sorted directly in accordance with the IVR ratio principle, but without requiring automatic gain control for performing the equivalent of the electrical division.

Another object of the invention is to provide maximum signal-to-noise ratio and maximum circuit efficiency. A corollary of this object is to avoid the need for a radio frequency carrier for the color modulated reflectance signals. The signals representing the differences between the reflectances at the two wave lengths (the numerator of the IVR ratio) are applied directly to signals which are equal to or are a function of the average of the reilectances at the two wave lengths, and are applied in a manner that requires no electrical division as such, and requires no radio frequency carrier. This not only simplifies the circuit, but improves the signal-to-noise ratio, and renders the circuit less sensitive to maladjustments.

Another feature of the invention is the simplicity of the circuitry involved. The reflected light beams of the two wave lengths selected, are received alternately, there being a total of 3600 individual light pulses per second. This gives a cyclic frequency of 1800 cyles. Alternating current components of the voltages that represent the differences in reflectances, are developed independently of, and are combined with, direct current signal components. The direct current signal components represent either the average reflectance, or at least one of the refiectances. The alternating and direct current signal components are combined with a grid bias voltage. This combination is made in such a manner that signals proportional to the IVR ratio can be picked off the signal circuit by a series of potentiometers, each potentiometer having been set for an adjustment between two successive grades of fruit.

Each potentiometer is associated with a thyratron tube, so that as successive mid grade points are reached, the thyratrons are successively fired, first one, then two, then all three (for example), and each one of these situations is sensed and acted upon as indicating the classification for a selected grade point. In the form of the invention to be described, fruit lying between one extreme (full ripe, or yellow) and the next most nearly mature grade does notfire any thyratron. Other grades do result in the firing of one or more thyratrons. The means by which the reflected light pulses, sensed by the phototube and converted into voltage pulses, are combined and utilized by the potentiome'ters, provides a very simple circuit that produces the IVR ratio directly as a basis for classification, but does not require an automatic gain control circuit.

Another objectof the invention is to provide a linear, or reversible system, which works in principle just as well when the article is illuminated directly and the reflected light source is modulated (broken into beams of two wave lengths that are sensed by the phototube) as it does when the light source is first modulated and these modulated wave lengths are reflected from the object under inspection and directed to the phototube. Stated differently,

' with the system of this invention, the basic circuit can be 'used'in either of two ways.

One method projects inte grated illumination light directly on the object under inspection, and modulates the reflected light for measurement. The other method modulates the light first, proj'e'cts the modulated light on the object, and uses the modula'te'cl light, as reflected from the object, as a source for measurement. Each of these systems has its own characteristics and advantages, and either can be used with the basic circuit of this invention.

The manner in which these and other objects and advantages can be obtained will be apparent from the following description of the invention as it is employed in "connection with the sorting of lemons by color.

unit that modulates the reflected light.

FIGURE 3 is a view of the vibrating wire unit taken looking in the direction of arrows 33 of FIGURE 2. FIGURE 4 is a diagram of the signal portion of a circult that provides the IVR ratio signal, the circuit including a series filter for the DC. signal components.

FIGURE 5 is a diagram showing the fixed bias voltage.

FIGURE 6 is a diagram showing the electrical pulses which "are proportional to the reflectances at two wave lengths and the corresponding A.C. component.

'FIGUR'E 7 shows the AC. voltage component isolated relatively to'an average voltage reference line.

FIGURE 8 shows the pulsating DC. voltage component ofthe electrical signals.

FIGURE '9 shows the average DC. voltage signal.

FIGURE IOshoWsthe negative bias, the average DC, and the AC. signals combined.

'FIGURE 11 shows the DC. pulses when the potentiometer that taps off the combined signals is set at midrange, reducing the DC. reflectance signals by a factor of K.

FIGURE 12 shows the sum of the signals with the DC. signals reduced, as in FIGURE 11. FIGURE '1 3 shows a combination of signals similar to that of FIGURE except that'the circuit that adds the signals does not include a series filter.

{FIGUREM shows the actual shape of a typical signal curve as a lemon enters the inspection station, passes through iea'nd leaves it. 7

FIGURE 15 is a combined mechanical and electrical circuit diagram of the system, the circuit including a series filter circuit in the signal combining circuit.

' thus alternately eclipse the two light beams.

FIGURE 16 shows a signal circuit that does not have a series filter circuit across the potentiometers.

FIGURE 17 is a composite pulse diagram showing derivation of the IVR ratio in the system of this invention when a series filter is employed in the signal cornbining circuit.

FrGURE 18 is a similar composite diagram when the signal sensing circuit includes no series filter circuit across the potentiometers.

FIGURE 19 is a view similar to FIGURE 1 showing a modified form of optical system.

THE MECHANICAL AND OPTICAL SYSTEMS Referring to FIGURES 1-3, the lemon L under inspection is supported by conveyor means 19 in the form of a rotatable carrier C. The carrier C and support 10 for the lemon form part of a system for receiving lemons at the desired rate of inspection, transporting them across the inspection station, carrying them past the classification bins, and releasing them into the proper bins. Details of such mechanism are not part of this invention and a suitable mechanism for this purpose is described in the copending patent application of Verrinder, Serial No. 605,797, filed August 23, 1956, entitled Article Handling Apparatus and Method, and assigned to the assignee of the present application.

The inspection station includes a generally spherical housing 11, in which is mounted a plurality of lamps 12 that give a generally white light illuminating source. These lamps may be standard automobile head light lamps, and there may be a number of them disposed around the internal surface of the spherical housing 11. The spherical housing serves to integrate the light in the sense that the light is reflected back and forth so that it illuminates the entire surface of the lemon quite unirormly. Light from the surface of the lemon passes through opposed lenses 13 mounted in the spherical housing '11, and impinges upon opposed mirrors 14 which converge the light onto a split or hybrid mirror 16 that bisects the angle between mirrors 14. The mirror 16 acts as a mirror for the left hand beam, as it is seen in the drawing, and transmits the right hand beam. The beams combine and impinge upon a masking plate 18 which is formed with spaced slits 19 and 19a. These slits produce light beams which may be about 15 millimicrons Wide, and these bands are spaced about 50 millimicrons apart. A vibrating wire 21, which is wider than the slits i9 and 1%, is caused to pass rapidly back and forth behind the slits, to alternately obstruct the slits and The result is that the light beams pass the wire 21 alternately, in one of two slightly angularly different directions.

In order to vibrate the wire 21, the wire is mounted on an aluminum frame 22 (FIGS. 2 and 3) by means of clamp 23 and a spring tensioning lever system '24. A coil 25 is mounted to surround the frame 22 and receives electrical energy from an oscillator 26 running at 1800 cycles. The coil 25 induces alternating currents in the closed loop formed by the wire 21 and the frame 22 and these currents coact with a permanent magnet 27, the poles of which are close to the wire 21. The result is that the wire is alternately deflected in the direction of the double arrow 20 on FIG. 2. This causes'the wire to vibrate across the slits 19 and 15 11, at a frequency-of 1800 cycles. The details of this means 'for eclipsing the two beams are not part of this invention. As will be seen as this detailed description proceeds, the geometry of the wire diameter and slit spacing is such that there are no voltage peaks other than the fundamental peaks derived from the modulation of the reflected light. For example, a rotary disc having adjacent apertures at different radii, of the type disclosed generally in the aforesaid Powers patent, may be employed.

The two angularly disposed beams of light reflected from the lemon L are collimated bylens 28 (FIG. 1) and pass through a prism 29. Since these beams strike the resonate at 1800 cycles.

v3 prism at slightly different angles, the beams will emerge from the prism as beams of different wave lengths. The wave length of each beam depends upon the geometry of the apparatus, including the spacing of slits 19 and 19a. As mentioned, it has been found that Wave lengths in the red and infrared region are most effective for the color sorting of lemons, a red wave length beam of 6780 A. and an infrared wave length beam of 7200 A. having been found to be suitable for the purposes of this invention.

After leaving the prism 29, the beams of both wave lengths are directed by a lens 31 so as to pass through a slit plate 32 into a collimator 33, whereupon the beams alternately impinge upon the cathode of a photomultiplier tube V1. The tube converts the alternate beams that it receives into a series of corresponding voltage pulses, available at the anode of the tube.

In order to supply plate voltage to thyratrons in the control circuit at the proper time, a cam 34 driven by the conveyor system C operates a switch 36 connected to a voltage source (not shown). Similarly, in order to supply voltages to the release system at the proper time, another cam 37 operates a switch 38 in synchronism with conveyor motion.

ELEMENTS OF THE SIGNAL AND CONTROL SYSTEMS FIGURE is a diagram of the signal and sorting or control circuits, a conveyor and inspection system, a memory device, and a release system. Details of the conveyor, memory and release systems are not part of the invention. In the signal and control circuits, the cathode of the photomultiplier tube V1 receives the reflected light from the lemons under inspection, and converts them into voltage pulses R1, R2 alternately. The dynodes of the photomultiplier tube are supplied from a minus 1000 volts DC. potential source connected to the anode of the tube, by means of a voltage divider string, including a series of equal resistors 41. The anode sorting voltage signals R1, R2 are connected to end terminals of potentiometers 42, 43, and 44 forming part of the signal circuit. Included in the signal circuit in series with the potentiometers 42, 43, and 44 is a parallel resonant circuit 45, including an inductance 46 and a condenser 47, tuned to resonate at the modulating frequency of 1800 cycles. A bias voltage source 48 supplies a negative bias voltage which may be about two volts for the thyratrons employed. It is important to note that the bias voltage source 48, the tuned circuit 45, and paralleled set of potentiometers 42, 43, and 44, are connected in series between ground and the anode of the photomultiplier tube V1. In the form shown in FIG- URE 15, a series resonant filter circuit a is connected across the potentiometers, which circuit includes a condenser 47a and an inductance 46a in series, tuned to The Q of this circuit is not high.

The resultant signal voltages tapped from potentiometers 42, 43, and 44 reach the grids of thyratrons V2, V3, and V4 by means of grid resistors 49, 51, and 52, respectively. The plate voltages of thyratrons V2, V3, and V4 are supplied through plate load resistors 53, 54, and 56, respectively. These load resistors connect through a resistor 57 to a 200 volt D.C. plate supply by means of switch 38, previously mentioned. The manner by which the thyratrons V2, V3, and V4 are fired will be explained later in this description.

MEMORY AND RELEASE CIRCUITS A memory device M is provided in the system. This device is necessary because the release stations are spaced some distance along the conveyor mechanism from the inspection station, so that release signals generated at the inspection station are actually applied to signal sensitive devices at the various release stations after elapse of the appropriate time. In the memory device M illustrated,

a rotatable drum 58 forms the body of the device and has mounted therein a series of capacitors 59. As indicated by dashed line in FIGURE 15, the memory device M is connected to rotate in synchronism with the conveyor mechanism C. Each capacitor 59 has one plate thereof connected to a commutator segment 60 at the periphery of the drum 58. Segments 60 are engaged by a brush 61 connected between resistor 57 and resistor 56 in the 200 volt supply line. Brush 61 introduces the release signals to the memory device. The other plates of the capacitors 59 are grounded at 62.

Only the yellow lemon release system, indicated at 63, is detailed in FIGURE 15. It includes a thyratron V5 which actuates the release mechanism when fired. In order to transmit the release signal from the memory device M .to the release circuit, a brush 64 is provided that engages the segments 60 of the capacitors 59 in the memory unit. The brush 64 connects .to an input diode 65, and to a plate voltage blocking diode 66, connected to the plate of the release thyratron V5. These diodes prevent charging of the memory device capacitors by the various positive voltage sources connected to the release circuit. There is a positive DC. signal bias voltage of 175 volts for the yellow release system, which voltage is introduced by means of a resistor 67.. A condenser 68, connected between the signal input diode 65 and the grid of the release thyratron V5 isolates the grid of the thyratron from the 175 volt DC. signal bias voltage. The grid of the thyratron is connected through a resistor '71 to a minus 10 Volt DC. grid bias source. Diode 69 is connected across resistor 71 in order to permit rapid changing of capacitor 68.

The plate of the yellow lemon release thyratron V5 connects through the coil 72 of a release relay switch S to the plate voltage applying switch 36 previously mentioned. When switch 36 is closed, it connects a source of 300 volts DC. to the plate of the thyratron, and if the proper signal is received by the grid, the thyratron fires, resulting in actuation of the relay switch S. The contacts '73 of the switch S, when closed, operate an air valve 74 which has a nozzle 76 that actuates a trip mechanism 77, for releasing the lemon L from its support mechanism 10, when the lemon L is classified as being yellow.

In addition to the yellow release circuit 63, a brush 78 connects to a silver release circuit 79 which, in the illustrated example, receives a signal bias of plus 150 volts D.C. Similarly, a brush 81 connects to a light green release circuit 82, that receives a signal bias of plus 125 volts D.C. Finally, a brush 83 connects to a dark green release circuit 84, that receives a plus volts DC. signal bias. Each of the release circuits has a Ielease thyratron and a release relay connected to release means at the associated release station. Each release circuit receives the minus 10 volts D.C. thyratron grid bias for its thyratron. There will be as many release stations as there are lemon grades to be segregated.

The operation of the control signal system of FIG- URE 15 will now be explained, except for the signal producing portion of the circuit. Assume that the signal producing portion of the circuit provides a signal such that none of the thyratrons will fire. This is the situation present when a yellow lemon is under inspection. Under these conditions, the voltage between resistors 57 and 56, that is, the voltage at the signal introducing brush 61, will be plus 200 volts DC, as indicated in parenthesis at this junction. This is because when they are not firing, the thyratrons, V2, V3, and V4 act as open circuits in the 200 volt supply. While the lemon is at the inspection station, switch 38 will close under control of the cam 37 to supply the control voltage, determined by the condition or" the thyratrons (plus 200 volts in this case) to the memory device. As mentioned, when a yellow lemon passes the inspection station, there is no signal developed suflicient to fire any thyratron. Under these conditions,

' air valve 74 to release the yellow lemon L.

later in this description. 'there is a voltage drop through the plate load resistors 53, 54, 56, so that the control signal voltage applied to brush 61 is now, in the example, plus 175 volts D.C., thisbeing indicated in-parenthesis at the right of thyratron 'silver release station.

switch 38 connects the full 200 volts DC. source to the brush 61 of the memory device. This charges the particular memory capacitor 5 that is now electrically connected to the brush, to a potential of substantially 200 volts. The actual potential reached by the memory capacitors depends upon the length of time they make electrical connection with the brush 61. For ease of understanding it is assumed that the memory capacitors almost reach the signal potential, but if the speed of the memory device is so great that they leave with a lower charge, this means only that the signal bias voltage must be adjusted accordingly. Before the next memory capacitor 59 reaches brush 61, the switch 38 will open, removing the 200 volt D.C. source from the plates of thyratrons V2, V3, and V4, thereby extinguishing any thyratrons that might have been fired.

As the lemon proceeds along the conveyor, the memory device M rotates in synchronism with the conveyor, and when the previously charged memory capacitor 59 reaches the yellow release brush 6 5, a 200 volt positive pulse is applied to the right hand plate of the condenser 68 in the grid circuit of the yellow release circuit thyratron V5. This pulse of 200 volts is 25 volts more positive than the 175 volt signal bias applied to the left hand plate of condenser 63 by means of the 175 volt signal bias source. A resultant 25 volt positive pulse appears across condenser 68 and is sufiicient to drive the grid 'of the thyratron positive, overcoming the minus 10 volt DC. bias thereon, whereupon the thyratron fires. When the thyratron fires, the contacts 73 of the yellow release switch S close, as illustrated in the diagram, operating Immediately thereafter, the cam 34 will open switch 36 to extinguish the thyratron V5 by disconnecting the relay coil from the 300 volt plate supply.

If a silver lemon is under inspection, the signal system will fire thyratron V2, because of the nature of the signal produced by a silver lemon, as will be explained in detail When thyratron V2 conducts,

V2. This plus 175 volt control signal has the same potential as does the plus 175 volt signal bias voltage applied to the yellow release circuit, so that when the active memory condenser 59, now charged to plus 175 volts D.C., reaches the yellow release circuit brush 64, it has no effect on the circuit and the lemon under in- However, as the same charged condenser 59 continues circuit, and here the signal bias is only plus 150 volts DC. Therefore, the 175 volt charge on the memory condenser is sufiicie'nt to overcome the 150 volt DC. signal bias, and the resulting pulse drives the grid of the silver release thyratron (not shown) positive, thereby firingthe thyratron and releasing the silver lemon at the Any charge remaining on the memory condenser 59 is insufficient to fire the light green and dark green release circuit thyratrons.

When alight green lemon is under inspection, the output of the signal input is such that boththyratrons V2 and V3 will fire, thereby dropping the control signal voltage applied to brush Gland to active condenser 59,

'to 150 volts, as indicated in parenthesis at the right of thyratron V3. This 150 volt charge will not fire the ''yellow orsilver release circuits, as the condenser passes them, for reasons given, but Will fire the light green release circuit when the condenser reaches the brush 31 leading to that circuit.

'fire, dropping the control signal voltage applied to the signal input'brush 61 to 125 volts. In this case, none-of the yellow release, silver release, and light green release circuits will be actuated as the charged memory capacitor sweeps by these circuits, but the dark green release circuit thyratron will fire, to release the dark green lemon into its proper receptacle.

The various power supplies for the photomultiplier tube, the plates of 'thynatrons V2, V3, V4, and V5, and the other thyratrons in the release circuits can be of conventional design and since the details thereof are not part of the invention, thy are not shown. Typical circuit values for the circuit diagram of FIGURE 15 are given in Table I below.

Table I.Typical circuit components Reference is now made to FIGURES 4,l4. FIGURE 4 is a separate diagram of the signal circuit 45. The optical system and the photomultiplier tube can be considered to act functionally as a rapidly acting switch which supplies alternate voltage pulses R1, R2, corre sponding to the two reflect-ances, to the circuit at a rate of 1800 cycles. Stated differently, in one second there will be 1800 R1 voltage pulses each alternated by an R2 voltage pulse, and one cycle is considered to consist of one of each type pulse. The signal circuit can be considered as dealing with three separate voltages, all of which. are combined or added to produce the desired IVR ratio signal. These voltages are a minus 2 volt'bias voltage, an alternating current voltage, e and a negative direct current "oltage, 6 The 2 volt bias voltage is merely the-cut off voltage for the grids of the thyratrons, and it will be assumed that when the net voltage on the grid of a thyratron is more positive than minus 2 volts, the thyratron will fire.

The manner in which the signal circuit 45 produces signals that represent the IVR ratio for controlling thyratrons V2, V3, and V4, will now be explained. As seen in FIGURE 6, the voltage pulses R2 corresponding to one of the two reflectances are more negative than the minus '2 volt bias voltage, and pulses R1, correspon ing to the other reflectances, are still more negative than the bias voltage. These pulses are-applied across the Potentiometers (only the potentiometer 43 being illustrated in FIGURE 4). The pulses R1 and R2 are negative because current flow in the photomultiplier tube is from the anode'toward the negatively connected cathode, as seen in FIGURE 15. Since all of the potentiometers are in parallel, the same voltage pulses aregenerated across them all. In the form of signal circuit shown in FIGURES 4 and l5, the potentiometers are bypassed by Qt source of minus 2 volts, which is supplied by a battery or other voltage supply, the positive side of the supply being grounded.

Examining the voltages developed at each of these series connected signal elements individually, as indicated in FIGURE 5, the minus 2 volt fixed D.C. bias voltage can be considered as a straight line reference to ground. FIGURE 6 shows the two reflectance voltage pulses R1 and R2, voltage R1 being more negative than R2. These voltages are shown referenced to the minus 2 volt bias line in this and in other figures. The voltage differences between the pulses R1 and R2 provide an alternating voltage component centered about a reference line labeled O'V. The alternating signal component is shown isolated in FIGURE 7 about the O'V reference line, as an A.C. voltage having a peak to peak value e The magnitude of the alternating signal voltage e is independent of the location of its reference line OV, since the alternating signal voltage is almost entirely developed across the tuned circuit, which has a very high impedance at the signal frequency of 1800 cycles. This A.C. signal voltage is applied to one of the fixed terminals of the potentiometer, and its magnitude as sensed at the slider of the potentiometer, is independent of the potentiometer setting.

Referring to FIGURE 8, it can also be seen that the pulses R1, R2, have a pulsating or square wave type D.C. component, having an average value e referenced below the minus 2 volt bias line. The pulses are not actually square waves, but they are drawn substantially as such for convenience of illustration. Their shape, as does the shape of the reflectance pulses themselves, depends upon the physical nature of the beam eclipsing device. The average value, e of the pulsation D.C. component of the signal is shown in FIGURE 9 as displaced from the -2 V. bias voltage by a minus D.C. voltage indicated as a When the potentiometers are shunted by a series resonant filter circuit 45a, it is the average D.C. signal, and not the ripple current that will combine with other voltages in the signal circuit.

FIGURE 10 shows diagrammatically how the signal circuit combines or adds the three voltages involved, namely, the minus 2 volt bias voltage, the negative average D.C. voltage component e and the A.C. component e These voltages, as added in FIGURE 10, are those that would appear across the fixed terminals of the potentiometer 43, that is, across the entire potentiometer resistor.

In actual practice, the potentiometers are usually adjusted so that only a portion of the D.C. signal component e is applied as the thyratron grid signal. Referring to potentiometer 43, by way of example, this is shown in FIGURES 4, 11 and 12, wherein the D.C. volttage resulting from pulses R1 and R2, and developed across the entire resistor of the potentiometer, is actually taken off at the slider of the potentiometer. Such voltage is reduced by a factor K, corresponding to the setting of the potentiometer. The potentiometer is assumed to be set at mid-range in this example. Under these circumstances, the pulses KR1 and KRZ, and the resulting average D.C. voltage labeled e in FIGURES 4, 11 and 12, will be less than the corresponding D.C. signals e (FIGS. 4 and 10) developed across the entire potentiometer.

FIGURE 11 shows the combination of the negative bias voltage -2 V, (FIG. the A.C. component e Y (FIG. 7), and the average D.C. component e which has been reduced from the total value e (FIG. because the potentiometer has been set to represent a factor K. This factor K is assumed to be such that the positive peaks of the A.C. component e just reach the negative 2 volt critical bias line, as seen in FIG. 11. Under these circumstaonces, the associated thyratron will just fire or will be just on the verge of firing.

If the series resonant filter circuit a is omitted from the signal circuit, the D.C. signal components will be sensed by the potentiometer as a pulsating voltage (IR drop) and will be so combined with the other signal voltages. Such a circuit is shown in FIGURE 16, and the result of the combination of voltages with this circuit is shown in FIGURE 13. As seen in the latter figure, the positive half cycle peaks of the A.C. component are now superimposed upon the positive peaks of the pul sating D.C. component. Thus the firing of the associated thyratron under these conditions will be represented by a dilferent setting of the potentiometer. The results of this circuit can be rationalized in another way, in that it can be considered that the positive half cycles of the A.C. signal are added algebraically to'the negative D.C. pulses KRZ, developed across the potentiometer between the point of connection of the fixed terminal with the tuned circuit and the slider of the potentiometer. The result is the same in either case.

The curves shown in FIGURES 6-13 represent only a portion of the entire reflectance signal curve that is generated as the lemon passes into and out of the inspection station. The complete signal for a single lemon has the general shape shown in FIGURE 14. This can be understood when it is recognized that the lemon passes into, through, and out of the illuminated inspection zone. At first only a small portion of the lemon produces reflectances and corresponding IVR ratio signals. As more and more of the lemon area passes into the zone, the refiectances increase, as do the corresponding voltage signals, and as the lemon leaves the zone, they decrease. This gives the envelope of the A.C. and D.C. components of the signal curve the lemniscate form shown in FIG- URE 14.

Thus the direct current signal actually pulsates at the inspection frequency which may be in the order of 40 lemons per second.

CONVERSION OF VOLTAGE SIGNALS TO CONTROL SIGNALS The conversion of the voltage signals generated in the signal circuit to control signals will now be descirbed, employing two examples. Referring to FIGURE 15, it is first assumed that a yellow lemon is under inspection. At the juncture of the tuned circuit with the potentiometer 42, the A.C. component of the signals, as developed across the parallel tuned circuit 45, will be centered about the two volt bias line, as illustrated in the waveform diagram 116, placed at the upper center of FIGURE 15. In other words, the A.C. signal component can be considered as alternately raising and lowering the potential of the entire set of Potentiometers, or as an A.C. generator connected in series with the potentiometers.

There is no thyratron provided for a yellow lemon classification, but the lemon closest in color to the yellow lemon is a silver lemon, and there is a silver lemon thyratron V2 controlled by the setting of potentiometer 42. This potentiometer will be set so that when a yellow lemon is under inspection, the D.C. signal component of the signal, as tapped off by the potentiometer, is such as to place the positive peaks of the A.C. component below the critical bias line of minus 2 volts, as illustrated at 117. Thus the yellow lemon signal will not fire the silver lemon thyratron V2.

As shown at 118, the potentiometer 4.3 for light green lemons is set to further depress the A.C. component below the bias line, so that there is even less chance of the green lemon thyratron V3 firing, when a yellow lemon is under inspection. Similarly, as illustrated at 119, the potentiometer 44 for the dark green thyratron V4, is set to still further depress the A.C. component of the signal below the bias line, so that the dark green thyratron V4 also remains out 01f.

Thus with the proper settings of the potentiometers, a yellow lemon will not fire any of the thyratrons. When no thyratrons are fired, the yellow release circuit will be 'green lemons. :green lemon potentiometer 44 is set so that the positive thyratrons fire.

i. i brought into action. When the yellow release thyratron V5 fires, its plate potential is lowered and this discharges the previously applied 200 volt charge on the memory condenser to a .potential below that sufiicient to trigger the remaining release circuits, so that the yellow release circuit, and only the yellow release circuit, is energized.

When a silver lemon is under inspection, the AC. sig- 'nal components have more amplitude than do those for a -yellow lemon. the silver lemon potentiometer 4-2, the AC. component With the previously assumed setting of is now adequate to fire the silver lemon thyratron V2, because the DC). signal component for a silver lemon,

asta'pped off by potentiometer 42, cannot drop the positive peaks of the AC. signal component below the critical 'bias voltage.

However, the potentiometers 43 and 44 are set so that the DC. signal component will depress the AC. peaks developed when a silver lemon is under inspection suflicientlylso that the light green thyratron V3 and the dark green thyratron V4 remain cut oil. Since thyratron V2 has fired, the control signal voltage (175 volts) is too low to fire the yellow release thyratron V5, but the silver release circuit will be energized. As before,

thereis not enough charge left on the memory condenser ;to trigger the light and dark green release circuits that follow.

Similarly, when light green lemons are under inspection, the light green potentiometer 43 has been set so that the D.C. signal component will not depress the AC. signal component sufficiently to prevent firing of both the .silver lemon thyratron V2, and the light green lemon thyratron V3. However, the dark green potentiometer ages for a dark green lemon is greater than that for a yellow lemon, and although this is not illustrated, the amplitude is also greater than that for silver and light As shown at 121, 122, and 123 the dark peaks of the A.C. signal for dark green lemons will reach and go slightly above the 2 volt bias line for the dark green thyratron V4 as well as for the other two thyratrons, so thatthyratrons V2, V3, and V4 will be fired. This reduces the control signal to 125 volts, which is sufficient to actuate the dark green release circuit but none of the other release circuits, in the manner previously described.

To recapitulate, when a yellow lemon is inspected, none 7 of the thyratrons fire. When a silver lemon is inspected,

only the silver lemon thyratron V2 fircs. When a light green lemon is inspected, thyratrons V2 and V3 fire, and

when a dark green lemon is under inspection, all three 7 As indicated inparenthesis at the right of each thyratron in FIGURE 15, as the number of thyratrons that fire increases, the control signal voltages applied to the memory device correspondingly decrease,

because the firing of each thyratron introduces an additional voltage drop across the plate load resistors of the thyratrons. 'Tlhis'progressive decrease in voltagesapplied tothe memory deviceresults in a corresponding shifting in the release-that'is actuated, from the yellow release with no thyratrons firing to the dark green release with all thyratrons firing.

HOW THE SIGNAL CIRCUIT PRODUCES IVR RATIO SIGNALS The advantage ofusing'the IVR ratio as a means for producing controlling signals for color sorting have been explained, and it has been stated that in accordance with i this invention, the IVR ratio principle is employed by a simple circuit, which does not require electrical division as such, and requires no such expedients such as employment of an automatic gain control circuit. The fact that applicants series signal producing circuit operates on the IVR ratio principle whether or not it includes a series resonant filter circuit 450, is demonstrated in FIGURES 17 and 18.

Referring to FIGURE 17, the signals are illustrated diagrammatically in the case wherein a series resonant filter circuit is connected across the potentiometers in the signal system, as shown in FIGURES 4 and 15. The left portion of FIGURE 17 shows the voltage pulses R2 and R1 (corresponding to the two reflectance measurements) as developed across the terminals of the potentiometers. In other words, the full D.C. signal voltage components are shown. For ease of understanding, the zero voltage reference line is omitted in these figures and the reference line is arbitrarily established as that of the minus 2 volt bias line. It is also to be understood that should the positive half cycles, or peaks, of the A.C. signal components become more positive than the minus 2 volt bias line, the thyratrons will fire. Referring to the left portion of FIGURE 17, the average negative DC. component c is shown. This is a component that will be sensed by the system when the series resonant circuit is shunted across the potentiometer. Superimposed upon the average negative DC. bias voltage line, is the alternating signal component e The value of the average D.C. component e is half the sum of the voltage pulses R1 and R2, that is The amplitude of the positive half cycles of the AC. components is half the difference of the pulses R1 and R2, that is,

RlR2

Assume now that one of the potentiometers such as 43, is set to tap off a fraction of the average D.C. component. In other Words, the DC. signal voltage as applied to the thyratron is reduced by somedesired amount, that is, by a factor of K2. This is illustrated in the diagram forming the right portion of FIGURE 17, wherein the DC. signal components are now KZRI and KZRZ, respectively. This reduction of the 11C. signalcomponent, as applied to the grid of the associated thyratrons by means of the center tap of the potentiometer, has anegligible effect on the amplitude of the A.C. signal components, because the latter are generated across the high impedance parallel tuned circuit and not across the potentiometer. Thus, the amplitude of the A.C. signal component remains unchanged. With the setting of the potentiometer illustrated in the right hand portion of FIGURE 17, the positive halfcycles of the AC. component rise above the minus 2 volt bias line, and the associated thyratron would fire. The amount that the positive A.C. component peaks rise above the bias line is indicated as a constant K3, and it can be seen that the value of K3 depends upon the settingof thepotentiometer. Obviously, the potentiometer canbe set so that K3 becomes negligibly positive, zero, or slightly negative. In any event, it can hemade equal to zero for purposes of analysis. Under these conditions it can be seen that the average D.C. component KZe determined by the potentiometer setting, can be made to equalthe positivehalf cycle of the A.C. signal component,

As indicated below the right hand portion of FIGURE 17, simple algebraic manipulation shows that this signal com- I3 bination is the equivalent of a fraction having a numerator that is the difference between the pulses (refiectances) or Rl-RZ, and having a denominator that is the sum of the same, or Rl+R2, and that the fraction itself is equal to a constant K2. This fraction is the IVR ratio, and it equals a constant that can be established by proper setting of the potentiometer for the grade lemon under inspection. It can also be seen that the denominator of the fraction can be made equal to the average reflectance,

by introduction of another constant. Thus without requiring electrical division, automatic gain control, or other expedients, the simple series additive type circuit forming the signal generating portion of this invention, makes possible lemon color sorting using the IVR ratio principle. The circuit has all of the advantages of selectivity and reliability characteristic of an IVR ratio system, and has the advantages in terms of circuit simplicity of systems employing coarser criteria, such as those that merely compare reflectances. Also an RF carrier, with its lack of efficiency, and poor signal to noise ratio is not required.

In FIGURE 18, substantially the same diagrams are shown, except in this case the series tuned filter circuit 45a is omitted, so that the DC signal component, as applied to the thyratron grids, is a pulsating DC. signal. As seen at the left of the figure, the least positive D.C. component of the pulsating DC. signal is the R2 pulse itself, labeled e The A.C. component c is substantially unaffected by the presence or absence of the series tuned filter circuit, because it is developed across the high impedance parallel tuned circuit 45. Referring to the right hand portion of FIGURE 18, here the potentiometer has been set so that the smaller D.C. component R2 is modified to KRZ a negative voltage (the other component is now KRl), and the positive half cycles or peaks of the A.C. component are added to the negative voltage KRZ. As illustrated, the A.C. peaks rise above the negative 2 volt bias line by a factor K1. This would tire the thyratron, but again the potentiometer can be set so that the factor K1 is negligible, or zero. As shown below the figure, it can be seen that the signal system is operating on an IVR ratio basis, with the numerator of the fraction representing the difference between the pulses (R1R2) and the denominator representing one of the pulses, namely R2 in this case. As stated, this provides for operation on the IVR ratio principle, except that the denominator of the fraction, instead of representing the average reflectance as before, merely represents one of the two refiectances. However, in either case, the variations between grades is such that reliable color sorting can be obtained, which sorting will be independent of blemishes, variations in circuit constants, the presence of wax or water on the surface of the fruit, and other conditions that have heretofore produced inconsistent, unreliable operation.

Table II is a tabulation of reflectance values and IVR ratios from grade to grade using the system of FIGURE 17, wherein the average DC. voltage signal circuits of FIGURES 4 and 15 are employed. In this table the silver lemons have been divided into two grades, which is common practice. Means for sorting out only a single grade of silver lemon has been shown in the circuit of FIGURE 15 for simplicity. Using the IVR ratio system by means of the signal circuit of this invention has the advantages that a reasonably large number of grades can be assigned without the noise level of the system exceeding the useful signal level.

14 7 Table 11 (FIG. 17)

change Grade in IVR R2 6,780 at 7,200 A. A.

Dark Green 10 71 Light Green- 23 Silver A.

In Table II the fifth column shows the ratios between the IVR fractions from grade to grade, and it is seen that these ratios are all of the same general orderand therefore can be implemented reliably. The sixth column gives the decibel change in IVR (20 log Col. 5), which is a factor that is critical in instrument design, wherein an instrument must operate over a range of grades. It is important to note that the values in the sixth column are of the same order. The system represented by Table II is that in which the denominator of the IVR fraction represents the average reflectance of the fruit, that is, where the series resonant filter circuit is employed (FIGS. 4, l5, and 17).

Table III below resembles Table II except that the IVR ratio factor is now computed on a basis wherein the denominator of the fraction is one of the reflectances, R2 in this case. This corresponds to the diagrams of FIG- URES l6 and 18.

Table 111 (FIG. 18)

IVR R2 R1 6,780 A. 7,200 A. R1-R2 Dark Green. 10 71 61 6 Light Green--. 23 80 57 2. Silver A. 50 84 34 0.

The fifth and sixth columns of Table III wherein the ratios of the IVR factors and the decibel changes from grade to grade are given, show the decibel changes to be all of the same order. Data of this sort are subject to implementation, with reliability and accuracy.

Thus it can be seen that applicants apparatus although simple, provides for precise sorting between a fairly large number of grades, and is accurate at either end of the scale. In other words, it is sufficiently accurate at the mature or ripe fruit end of the scale (where color separation has proven difficult) to give results comparable to those obtainable at the green end of the scale. Because of the employment of the IVR ratio system, as mentioned previously, factors such as equipment aging, lemon size variations, color blemishes, the presence of wax or Water on the lemons, and other factors not directly attributable to color differences alone, are cancelled out in the system. The system does not require direct electrical division or automatic gain control, nor does it require the use of modulated RF carriers, with their inefliciency and the low signal to noise ratio, characteristic of such systems.

MODIFIED OPTICAL SYSTEM The signal gathering or combining system of this invention having been described, and since it has been shown that the invention involves a series circuit wherein various voltages are combined directly and simply, it can now be seen that the system is what might be termed a linear system. That is, it is relatively independent of the intermediate optical means employed to produce the measurement of reflectances upon which operation of the system is based. In the optical system of FIGURE 1, the lemon is illuminated in a spherical housing by a battery :of lamps providing an integrated and intense illumination, that gives a strong signal and insures reliable operation. However, in case it is not desired to subject the articlebeing classified to the heat generated by a strong illumination source, or for other reasons, some of which may be mechanical or relateto the apparatus in which the system is' employed, the optical system of FIGURE 19. may bel i In this system the spherical inspection housing 11a, instead of "containing a series of illumination lamps, mounts the photomultiplier tube VlA. This tube is shielded from direct reflection from the lemon L under inspection, by a plate 86.v The optical elements, including' the lenses, mirrors, prism vibrating wire and other parts are identical with the form of FIGURE 1, but their employment is generally reversed from that of the system of FIGURE 1. In the form of FIGURE 19, a single illuminating lamp 12a, which should be a powerful lamp such'as a projection lamp, is at the location that was occupied by the photomultiplier tube V1 in the form of FIGURE 1. With the modified system of'FIGURE 19, the broad spectrumlight source is first broken into the two narrow inspection beams of 6780 A. and 7200 A. by the vibrating wire 21 and slits 19, 19a. These beams are refl ected by means of the mirrors 14 and directed against the lemon L under inspection. In this form, when the beams enterthe inspection housing Illa from mirrors 14, they have already been split up into inspection beams of two colors or wave lengths. Thus, the lemon L rcflects to the surface of the integrating reflector 11a, light from beams of two different selected wave lengths and these reflected light pulses alternately impinge upon'the active surface of the photomultiplier tube VIA, which is connected into a circuit like that of FIGURE 15. The rest of the system operates exactly as does that previously described. It may be that the intensity of the reflected light pulses received by the photomultiplier tube VIA in the system of FIGURE 19 is less than that of the system of FIGURE 1, but the system nevertheless can be made to operate if a suitably sensitive photomultiplier tube and associated circuit is employed, and if :the source of illumination 12a is relatively intense. This system has several inherent advantages in that the object under inspection is not heated by abattery of powerful lamps. This might be of importance in'case the heat sensitive device is under inspection, or if the device'under inspection were to be passed slowly through the inspection station.

Although a memory device has "beenshown wherein the thyratrons V2, V3, and V4 have their plate loads in series, the thyratrons'can be connected to the plate voltage source so as to render them independent of one another, forlcontrolling a different type'memory device such as that: of the above mentioned Verrinder application. As mentioned, details of the memory device itself are not part of this invention.

' Thus, still another advantage of applicants signal combining system is apparentfin' that/it is a linear system,

i and permitsreve'rs'ed but complementary"installations of the light source andthe photomultiplier tube,

Inthe broader aspect's'of the invention, instead of switching between two'selected wave lengths of light reflected from the objects under inspection (FIG. 1'), or between' two selected object illuminating wave lengths (FIG. 19), a pair of photomultiplier tubes can be provided, each with a filter to convertthe light reflected from the object illuminatedwith white light, as in FIG. 1, into light at one of the se lecte d wave lengths, The electric signal outputs of the photomultiplier tubes will then be alternately supplied to the comparison circuit of either FIG. 4 or FIG; 15 by a conventional electronic switch,

f whic h suppliesfl800 signals from each photomultiplier tube'to the' comparison circuit each second.

In the, appended claims the term photoe lectric means v ,is intended to include devices'that receive electromagnetic v radiation in or'near the visiblelight region and produce an electrical signal .that isa function of the intensity of the radiation. Examples of such devices include vacuum photocells, photomultiplier tubes, photovoltaic cells, photoconductive cells, phototransistors and other devices having the above described function.

Vhile a particular embodiment of the present invention has been shown and described, it will be understood that the system shown is capable of modification and variation without departing from the principles of the invention and that the scope of the invention should be'limited only by the scope and proper interpretation of the claims appended hereto,

The invention having thus been described, that which is believed to be new and desired to be protected by Letters Patent is: 1. Apparatus for sorting objects by color comprising 1621118 for illuminating the objects, photoelectric means, means for directing the beams reflected from the objects to said photoelectric means as alternate beams of different wave lengths, said photoelectric means producing alternate voltage pulses respectively proportional to the intensity of the beams reflected from the objects at said wave lengths; signal means connected to said photoelectric means, said signal means comprising means for isolating the alternating component of said pulses to produce an alterntaing current signal, means for averaging said alternate pulses into a direct current signal, means for adding said alternating current signal and a component of said direct current signal to produce control pulse signals, and circuit means for converting said control pulse signals into classifying signals.

2. Apparatus for sorting objects according to color comprising an inspection station, means for presenting objects to be sorted to said station at a given frequency, means for illuminating the objects at said station, photoelectric means, means for energizing said photoelectric means with light reflected from the objects at two selected frequencies, means for producing composite electric signals in response to the reflected light received by said photoelectric means at each of said wave lengths, means for causing said signals to alternately represent the reflected energy at each of said Wave lengths at a frequency many times greater than said inspection frequency, said signals each having a component developed at said alternating frequency and a component developed at the object inspection frequency, circuit means comprising a first frequency responsive circuit for developing a maximum signal at the alternating frequency and a second frequency responsive circuit for developing a signal at the object inspection frequency and having a minimum response to the signal at the alternating frequency, means for providing an adjustable bias signal, and comparison circuit means for adding together the signal developed at the alternating frequency and a pro-selected portion of the signal developed at the object inspection frequency together with said adjustable bias signaLsaid bias signal determining a threshold signal required to produce classifying signals. I

3. Apparatus for sorting objects according to color comprising an inspection station, means for presenting objects to be sorted to said station at a given frequency, means for illuminating the objects at said station, photoelectric means, means for energizing said photoelectric means with'light reflected from the objects at two selected frequencies, means for producing composite electric signals in response to the reflected light received by said photoelectric means at each of said wave lengths, means for causing said signals to alternately represent the reflected energy at each of said wave lengths at a frequency many times greater than said inspection frequency, said signals each having a component developed at said alternating frequency and a component developed at the object inspection frequency, circuit means comprising a first frequency responsive circuit for developing a maximum signal at the alternating frequency and a second frequency responsive circuit for developing a signal at 17 the object inspection frequency and having a minimum response to the signal at the alternating frequency, and comparison circuit means for adding together the signal developed at the alternating frequency and a pre-selec'ted portion of the signal developed at the object inspection frequency to produce classifying signals.

4. Apparatus for sorting objects according to color comprising means for deriving an electrical pulse train of alternate pulses such that the ratio of the magnitude of two consecutive pulses is proportional to the ratio of the reflectances of the object measured at two predetermined wavelength band's, classifying signal generating means comprising a control circuit for combining the A.C. component of the entire pulse train with a signal proportional to the magnitude of individual pulses in said train to thereby produce a control signal from which the object class can be determined, and circuit means con nected to said control circuit for converting said control signal into a classifying signal.

5. Apparatus for sorting objects according to color comprising optical object-scanning means, photoelectric means receiving light from said optical means, and electrical classifying signal generating means receiving the output of the photoelectric means; said optical scanning means including means for directing light onto an object positioned for classification, and means for directing the light reflected from the object to the photoelectric means;

and optical means including means for modulating the light so that it is presented to the photoelectric means in a succession of pulses alternatively selected at a given fundamental frequency from two diflerent wavelength bands; said photoelectric means producing an output of corresponding alternate voltage pulses such that the ratio of consecutive pulses is proportional to the ratio of the object reflectances measured at the said wave length bands; and said classifying signal generating means comprising a control circuit for combining the A.C. component of the electrical pulses with a signal proportional to the magnitude of individual electrical pulses to thereby produce a control signal, said classifying signal generating means also including circuit means for converting said control signal into a classifying signal.

6. Apparatus according to claim 5, wherein the control circuit includes means for isolating the A.C. fundamental frequency component of the electrical pulse train to thereby reduce said pulse train to a DC. signal component proportional to the average of both pulses of a consecutive pair, means for algebraically adding said components, and means for adding a DC. bias signal to the resultant sum for producing the control signal.

7. Apparatus according to claim 6, wherein the control circuit includes a resonant circuit for receiving the electrical pulse train, and presenting a high impedance to the fundamental frequency component of the pulses so that the A.C. signal component of the pulse train appears as a voltage developed across said resonant circuit, and wherein said control circuit includes an electrical pulse averaging circuit for receiving the electrical pulse train to produce the DC. signal component as a voltage signal proportional to the average electrical pulse magnitude.

8. Apparatus according to claim 7, wherein the resonant circuit is connected in series with the averaging circuit and in series with said DC. bias signal, the averaging circuit comprising a classifying signal potentiometer having one end connected to the resonant circuit and the other to the photoelectric means and further comprising an AC; by-pass circuit connected across said potentiometer so that a substantially DC. voltage is developed across the potentiometer proportional to the average electrical pulse magnitude, the potentiometer tap thereby selecting a proportion of the potentiometer voltage as the DC. signal component and, in addition, receiving the sum of the bias and A.C. component voltages to thereby form the control signal.

9. Apparatus according to claim 8, wherein a plurality of said potentiometers are arranged in parallel to receive the electrical pulses from the photoelectric means, and wherein the circuit means for converting said control sig nals into classifying signals comprises a trigger circuit connected to the tap of one potentiometer, and taps on successive potentiometers being set so as to successively increase the proportion of the DC. signal component in the control signal so that successive trigger circuits will operate at successive control signal levels, the operation of the trigger circuits thereby shorting corresponding portions of the associated potentiometer so that the voltage developed across said potentiometer determines the color class of the object,

10. Apparatus according to claim 5, wherein the photoelectric means comprises a single phototube for receiving all the modulated light pulses from the optical means, said tube having its anode connected via the control circuit to the positive line, so that the electrical pulses are negative.

11. Apparatus according to claim 5, wherein the optical object scanning means includes means for directing a light beam onto an object for classification, means for collecting the light reflected from at least one side of said object means for passing the reflected light through the light modulating means, and means for directing the reflected light, after modulation, to said photoelectric means.

12. Apparatus according to claim 5, wherein the optical scanning means includes means for directing a light beam through the light modulating means and onto the object to be classified, and means for directing the modulated light reflected from the object to the photoelectric means.

13. Apparatus according to claim 5, wherein the light modulating means comprises a light chopping device for dividing the light passing therethrough into two beams, each beam comprising a train of uniform light pulses such that the pulses of one beam alternate with those of the other at said fundamental frequency, an optical device for receiving said beams and allowing to pass therethrough only that light which lies within a separate predetermined narrow Wavelength band for each beam and means for directing said beams to said photoelectric means.

References Cited in the file of this patent UNITED STATES PATENTS 1,840,500 Getfrken et al Jan. 12, 1932 1,872,258 Elberty Aug. 16, 1932 2,244,826 Cox June 10, 1941 2,393,631 Harrison et al. Ian. 29, 1946 2,436,104 Fisher et a1 Feb. 17, 1948 2,517,554 Frommer Aug. 8, 1950 2,623,432 Lange Dec. 30, 1952 2,933,613 Powers Apr. 19, 1960 3,004,664 Dreyfus Oct. 17, 1961 3,069,013 Neubrech et a1. Dec. 18, 1962 

1. APPARATUS FOR SORTING OBJECTS BY COLOR COMPRISING MEANS FOR ILLUMINATING THE OBJECTS, PHOTOELECTRIC MEANS, MEANS FOR DIRECTING THE BEAMS REFLECTED FOR THE OBJECTS TO SAID PHOTOELECTRIC MEANS AS ALTERNATE BEAMS OF DIFFERENT WAVE LENGTHS, SAID PHOTOELECTRIC MEANS PRODUCING ALTERNATE VOLTAGE PULSES RESPECTIVELY PROPORTIONAL TO THE INTENSITY OF THE BEAMS REFLECTED FROM THE OBJECTS AT SAID WAVE LENGHTS; SIGNAL MEANS CONNECTED TO SAID PHOTOELECTRIC MEANS, SAID SIGNAL MEANS COMPRISING MEANS FOR ISOLATING THE ALTERNATING COMPONENT OF SAID PULSES TO PRODUCE AN ALTERNATING CURRENT SIGNAL, MEANS FOR AVERAGING SAID ALTERNATE PULSES IN A DIRECT CURRENT SIGNAL, MEANS FOR ADDING SAID ALTERNATING CURRENT SIGNAL AND A COMPONENT OF SAID DIRECT CURRENT SIGNAL TO PRODUCE CONTROL PULSE SIG- 